1. Field of the Invention
This invention relates generally to the field of support frames for raising and lowering a load which is supported on the frame and, more specifically, to such a frame incorporating self-equalizing means which automatically distributes to points of the frame lifting forces which substantially match the load occurring at each of those points during raising of the frame. Even more specifically, the invention relates to an improved trailer, especially a boat trailer, incorporating such a frame, and even more particularly, to a pontoon-boat trailer in which the frame, in its lowered or collapsed condition, permits the trailer to be driven underneath the boat with its pontoons sitting on the ground and, then, permits the frame easily to be elevated to its upright trailering position even though the load on the rear of the frame may be much greater than that on the front of the frame.
2. Description of the Prior Art
Lifting boat trailers, per se, are generally well known, but they suffer several disadvantages. More specifically, such trailers operated by hydraulic systems are very expensive and complicated. Boat trailers having a front-mounted winch which applies a pulling force to the front end of the frame suffer from the disadvantages of requiring an unacceptably high force to be applied to the winch handle, causing bending of the frame members when such a high force is applied, and not being lowerable or collapsible to a sufficiently flat position to permit them to be driven underneath a pontoon boat sitting with its pontoons on the ground.
Lifting trailers have also been disclosed in several U.S. patents. For example, U.S. Pat. No. 4,221,420 discloses a boat-and-car trailer having a first support assembly for the car and a second support assembly for the boat. Two pairs of pivotal scissor arms are secured to opposite sides of the first and second support assemblies and are hydraulically actuated to raise the boat support assembly from a collapsed position to a boat-supporting position. U.S. Pat. Nos. 4,286,800 and 4,406,477 disclose boat trailers having a collapsible boat-supporting structure, with the latter patent disclosing a winch and a cable pulley system which is used to raise a boat-supporting frame. U.S. Pat. No. 3,974,924 discloses a boat trailer having an aft cradle which provides mechanical leverage to assist in loading and unloading a boat. U.S. Pat. No. 3,113,686, U.S. Pat. No. 4,318,632 and U.S. Pat. No. 4,365,923 further show the state of the art of lifting boat trailers.